This invention relates to apparatus and methods for producing laminated materials, for example such as are used in packaging.
Goods such as processed food, sweets, medication and liquids are often packaged in material which isolates them from water, gas, vapor, oil, chemicals and the like. This packaging material is usually decorated in order to distinguish the product from similar goods, for instance, or to provide directions for use, to list ingredients or to provide statutory information.
Typical material for this purpose is made from single or double layered transparent plastics over-printed with the desired design, with double layered materials offering better protection to goods.
In order to enhance the visual appeal of a package or to provide a degree of protection against counterfeiting it may also be desirable to add metallised effects, such as holograms, within such multi-layered material. The resulting laminated packaging material typically comprises a sheet of aluminium foil or holographic film sandwiched, and thus protected, between two sheets of transparent polyethylene or polypropylene, one or both of which could be over-printed with a design. This material is not transparent, however, due to the presence of the opaque metallised layer.
It would be desirable to have available a packaging material which includes a metallised layer but through which the contents of a package are visible. This can be achieved by sandwiching strips of metallised material, rather than whole sheets, between outer transparent layers. In the regions where the metallised layer is absent the material is thus transparent.
However, simply laminating strips of foil within two plastic layers is not feasible on a mass production basis. The final laminated material will not be of uniform thickness and this will be magnified when it is rolled up, for instance. It is therefore necessary for the middle layer to include strips of transparent material parallel and adjacent to the metallised material to provide a layer with as constant a thickness as possible.
A desirable laminated material will thus be of substantially uniform thickness, having five layers ie.:
(A) a transparent film made from a material such as polypropylene or polyethylene, probably decorated with a design; PA1 (B) an adhesive layer; PA1 (C) a layer consisting of a combination of parallel strips of different materials in the same plane or surface. These strips might be, for instance, lightline aluminium metallised or partially-metallised laminating foil, metallised polypropylene film, aluminium foil, or transparent polypropylene or polyethylene; PA1 (D) a further adhesive layer; and PA1 (E) a heat-sealable or heat-melting film allowing easy application for an automatic packaging system.
Laminated packaging materials are generally manufactured according to the following process. The materials which make up layers (A) and (C) are loaded onto separate supply rollers. Material (A) proceeds from its supply roller through a glue tank, where an adhesive layer (B) is applied to its back surface, and then through a drying tunnel. The strips which form layer (C) issue from the relevant supply rollers and meet material (A) emerging from the drying tunnel (A) at an assembly roller. Layer (C) is bonded to adhesive layer (B) to form a laminated material (AC) which is collected on a receiving roller.
To complete the packaging material, the laminate (AC) is removed from the receiving roller and re-loaded onto a supply roller. The process is repeated on material (AC), with adhesive being applied to layer (C) and heat-sealable film (E) being attached to form finshed product (ACE) laminate.
A significant problem when manufacturing laminated material in this way, however, is the alignment of the strips in layer (C). The strips, which might be of differing widths, will generally issue from separate supply rollers which might have drums of different diameters and different motor speeds. The different materials will tend to have different tensile strengths, different coefficients of friction, and different thicknesses.
During bonding at the assembly roller, aligning the strips in parallel on the same plane or surface without an overlap is a problem. Avoiding wrinkles, creases, breakage, and deformation of strips during lamination is also difficult. These problems, of course, cause wastage of materials and interruption of the production line. Furthermore, the alignment of the layers at the assembly roller is liable to change due, for instance, to vibration of the machine and for these reasons current machines and processes of manufacture are, in general, limited to just two strips.
There is thus a need for a laminating process in which the strips which make up layer (C) can be accurately aligned relative to layer (A).